Recently, a swallowable capsule endoscope has been proposed in a field of an endoscope. The capsule endoscope including an imaging function and a radio communication function is swallowed by a patient from a mouth for an observation of inside of various organs, and travels through inside digestive organs such as a stomach, a small intestine, or a large intestine by a peristaltic movement to capture an image of the inside of the digestive organs one by one, until the capsule endoscope is naturally excreted from a human body.
An image data captured inside a body by the capsule endoscope while the capsule endoscope travels inside the organs is transmitted one by one to the outside of the body by radio communication, and stored in a memory provided in a receiver outside the body, or displayed on a display provided in the receiver. A doctor, a nurse, and the like makes a diagnosis based on the image displayed on a display by using the image data stored in the memory, or based on the image displayed at the same time of reception, on the display provided on the receiver.
Since number of a series of images captured by the capsule endoscope is generally enormous, a great amount of time and efforts are required for the doctor, the nurse, and the like to observe the series of images for making a diagnosis. In response to the above circumstance, such a display device has been proposed that determines a level of similarity between two images and changes a display rate of the images based on the determination result, when an observation is performed by displaying the images based on the image data stored in the memory (see, for example, Patent document 1). The above display device is configured, by focusing on such a point that a number of similar images are sequentially captured when a travel speed of the capsule endoscope slows down, so that when the similarity between two images is low, the images are to be displayed at a slow-display rate, while when the similarity is high, the images are to be displayed at a high-display rate.    Patent Document 1: Japanese Patent Application Laid-Open No. 2004-521662